1. Field of the Invention
This invention relates to a process for dewaxing hydrocarbon oils, and particularly to a distillate dewaxing process.
2. Discussion of the Prior Art
Processes for dewaxing petroleum distillates have been known for a long time. Dewaxing is, as is well known, required when highly paraffinic oils are to be used in products which need to remain mobile at low temperatures, e.g., lubricating oils and jet fuels. The higher molecular weight straight chain normal and slightly branched paraffins which are present in oils of this kind are waxes which are the cause of high pour points in the oils and, if adequately low pour points are to be obtained, these waxes must be wholly or partly removed. In the past, various solvent removing techniques were used, e.g., propane dewaxing and MEK dewaxing, but the decrease in demand for petroleum waxes as such, together with the increased demand for gasoline and distillate fuels, has made it desirable to find processes which not only remove the waxy components, but which also convert these components into other materials of higher value.
Catalytic dewaxing processes achieve this end by selectively cracking the longer chain n-paraffins to produce lower molecular weight products which may be removed by distillation. Processes of this kind are described, for example, in The Oil and Gas Journal, Jan. 6, 1975, pages 69-73 and U.S. Pat. No. 3,668,113.
In order to obtain the desired selectivity, the catalyst has usually been a zeolite having a pore size which admits the straight chain n-paraffins, either alone or with only slightly branched chain paraffins, but which excludes more highly branched materials, cycloaliphatics and aromatics. Zeolites, such as ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38, have been proposed for this purpose in dewaxing processes, and their use is described in U.S. Pat. Nos. 3,894,938; 4,176,050; 4,181,598; 4,222,855; 4,229,282 and 4,247,388. A dewaxing process employing synthetic offretite is described in U.S. Pat. No. 4,259,174. A hydrocracking process employing Zeolite Beta as the acidic component is described in U.S. Pat. No. 3,923,641.
U.S. Pat. No. 3,755,138 describes a process for mild solvent dewaxing to remove high quality wax from a lube stock, which is then catalytically dewaxed to specification pour point.
U.S. Pat. No. 4,053,532 is directed towards a hydrodewaxing operation involving a Fischer-Tropsch synthesis product utilizing ZSM-5 type zeolites.
U.S. Pat. No. 3,956,102 is connected with a process involving the hydrodewaxing of petroleum distillates utilizing a ZSM-5 type zeolite catalyst.
U.S. Pat. No. 4,247,388 describes dewaxing operations utilizing ZSM-5 type zeolites of specific activity.
U.S. Pat. No. 4,222,855 describes dewaxing operations to produce lubricating oils of low pour point and of high viscosity index utilizing zeolites including ZSM-23 and ZSM-35.
U.S. Pat. No. 4,372,839 describes a method for dewaxing crude oils of high wax content by contacting the oils with two different zeolites, e.g., ZSM-5 and ZSM-35.
U.S. Pat. No. 4,419,220 describes a distillate dewaxing process utilizing a Zeolite Beta catalyst.
U.S. Pat. No. 4,575,416 describes a lubricating oil dewaxing process utilizing a zeolite catalyst having a Constraint Index not less than 2; an acidic catalytic material selected from the group consisting of Mordenite, TEA Mordenite, Dealuminized Y, Rare Earth Y, amorphous silica alumina, chlorinated alumina, ZSM-4 and ZSM-20; and a hydrogenation component.
Copending U.S. patent application Ser. No. 614,072, now abandoned, describes a lubricating oil dewaxing process employing a mixture of a medium pore zeolite and a large pore zeolite.
The entire contents of these patents and application are herein incorporated by reference.
It is thus apparent that there are catalysts in the prior art useful for dewaxing engine oil, and specifically for dewaxing distillate fractions. However, it has been found that the use of composite catalyst in distillate dewaxing processes result in higher yields under better reaction conditions than the prior art.
It is an object of the present invention to overcome the deficiencies of the prior art.
It is additionally an object of the present invention to provide an improved process for catalytically dewaxing a waxy distillate feedstock.
These and other objects are fulfilled by the present invention, which is disclosed below.